Step 3 shows a Item Number, you can send a different Item Number to your paypal form for each customer so you know which customer bought which item.

If you make a database and generate a random id for each purchase you can change the item id every time a user has bought a item by generating a unique random id and excluding the existing ids in the database.

Just another thing - you should use IPN if you have an SQL database to set the order or payment as confirmed - if the user closes the browser or goes to another URL before the "Thankyou" page, the data wont be classed as confirmed. IPN Fixes this by sending a command to the server as a background process, meaning it is updated in the database while the user is on the paypal site -

Step 3 shows a Item Number, you can send a different Item Number to your paypal form for each customer so you know which customer bought which item.

If you make a database and generate a random id for each purchase you can change the item id every time a user has bought a item by generating a unique random id and excluding the existing ids in the database.

Just another thing - you should use IPN if you have an SQL database to set the order or payment as confirmed - if the user closes the browser or goes to another URL before the "Thankyou" page, the data wont be classed as confirmed. IPN Fixes this by sending a command to the server as a background process, meaning it is updated in the database while the user is on the paypal site -